How to Diagnose and Clear Cloudy Swimming Pool Water

Co-authored by Rob Litman

Last Updated: March 10, 2023 Approved

Pool water has to be regularly treated to maintain a pristine and sanitary appearance. Disinfecting the pool weekly or biweekly, maintaining the pool filter, the area around the pool and maintaining the proper water chemistry are all key to keeping the water pristine and clear. The most effective method to clearing cloudy pool water is to perform a full treatment on the pool before using water clarifying agents.

Part 1

Part 1 of 2:

Diagnosing the Problem

1
Inspect the color of the water and conditions on the pool walls. Algal growth, molds, and buildup of body wastes from swimmers can all cause cloudiness. If the water is green or visibly contaminated biologically, avoid swimming in the pool and begin treatment to kill biological growth.
2
Purchase a pool test kit. It should measure alkalinity, calcium hardness, total, free, and combined chlorine, pH, and cyanuric acid. These levels all have impact on the clarity, safety, and sterility of pool water. Many low-cost kits only test for pH and free chlorine levels, which might not give you an accurate picture of the chemical situation of the pool water.^{[1]
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3
Test the swimming pool water using the kit. The two areas that are most likely to cause cloudy pool water are the pH and the calcium hardness, though low chlorine/can indicate biological contamination.
- Non-chlorine pool cleaner alternatives like bromine can be measured with a DPD test. Multiply the chlorine level by 2.25. Recommended levels of chlorine should be multiplied as well. This particular test is impacted by the density of the cleaning agent, and bromine is more dense by this factor. ^{[2]
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4
Check your pool filter for sediment buildup or malfunction. Buildup of sediment can interfere with the filtration and retention of particulate matter. Previous attempts to clean could have damaged the filter. You can monitor the filter for clogs by examining if the return pump in the pool has reduced pressure.
- Avoid using backwash cleaning methods with a sand-bed filter, as this can reduce filtration efficiency by loosening the filtration media, and might force the purchase of a new filter.
5
Clean the floor and walls of the pool. Vacuum any loose debris, scrub the sides and floor with a brush, and vacuum any loosened detritus. Run the pool filter for 8-12 hours to remove any flotsam and detritus that might be clouding the pool.
- A vacuum can do wonders for the color of your pool. Plus, a pool vacuum isn't very expensive—most models are less than $200.

Part 2

Part 2 of 2:

Treating the Water

1
Consider replacing your pool filter. If it is malfunctioning, or is a sand-bed filter, backwash cleaning methods could have damaged the filtration media. It is essential to continue pool maintenance, and any malfunction should be treated seriously. Check the lines and filtration media before deciding what to replace.
2
Clean the floor and walls of the pool. Vacuum any loose debris, scrub the sides and floor with a brush, and vacuum any loosened detritus. Run the pool filter for 8-12 hours to remove any flotsam and detritus that might be clouding the pool.
3
Treat the water chemically to remove small particle buildup. Loose colloidal particles cause cloudiness. They are either organic in nature (like algae) or mineral buildups (loose calcium). Adjust the chemicals to these ranges and run the pool filter system for another day before re-testing.
- Free chlorine: 1-2 ppm
- Combined chlorine: <.3ppm
- pH: 7.2 – 7.8
- Total alkalinity: 80 – 120 ppm
- Calcium hardness: 180 – 220 ppm (higher levels are acceptable up to approximately 400ppm)
4
Adjust the pH using a commercial acidifier or basify it with borax. Do not attempt to mix strong acids or bases in your pool or without eye and skin protection and respirators.
5
Shock the pool if combined chlorine levels (the total chlorine level minus the free chlorine level) exceed .3ppm. Combined chlorine is free chlorine that has reacted with an agent in the water to form chloramine, which produces a strong chlorine scent. Pool shock kits should raise the chlorine to over 30ppm.
- If your pH test kit uses litmus paper and produces a purple or off color, this may be due to high levels of chlorine. Test kits often have a reagent, typically thiosulfate, that will remove the chlorine and enable an accurate test.
- High levels of cyanuric acid can reduce chlorine’s efficacy as a sterilizing agent and can be reduced with dilution. ^{[3]
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6
Monitor the chlorine and bromine levels over several days for stability. High variance day-to-day indicates a chlorine demand problem. Monitor cyanuric acid levels, which acts as a stabilizer for chlorine to prevent UV degradation, and consider investigating your chlorinator or investing in one to ease the process of keeping your pool stable.
7
Adjust the total alkalinity of the pool using sodium bisulfate or muriatic acid. Add them according to the directions on the package according to the volume of your pool. The solutions should be dispersed and accomplished their chemical reactions within six hours of treatment. ^{[4]
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8
Adjust the water hardness of the pool using a water softener. You can also use dilution with softer water to soften the water. These are agglomerating solutions that work best in slightly alkaline water, and take several days for the full effect to be observed. ^{[5]
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Research source} The hardness of local water resources varies tremendously from area to area, and the strength and dilution of these products can be recommended by pool cleaning professionals.
9
Use a clarifier on the pool water according to the directions, if all else fails. Clarifiers are agglomerating solutions that bind to colloids from the water and bring them out of suspension, to be removed by vacuum or through the filter. These chemicals are called flocculents, and the process is referred to as flocculation. ^{[6]
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Research source} Continue filtering for without interruption until the water clears.
10
Use a second dose of clarifier, or a stronger clarifier chemical. and continue to run your filtration system if the pool has not cleared. Keep in mind that too much clarifier will actually work against the clarifying process; particles will repel one another rather attract, and the concentration of the clarifier will increase. Follow label instructions to the letter. Do not repeat more often than 2 additional times over the course of one week.
11
Vacuum and scrub the hard surfaces of the pool to remove any deposited sediment from the flocculation. Discoloration, buildup, or rust, is likely the result of water hardness or alkalinity changes, rather than the flocculent.
12
Call a pool cleaning professional in case of continued failure. Multiple treatments failing generally indicates a secondary, unseen problem that can be detected and treated most effectively and safely by a professional. Multiple cleanings can cause skin and mucous membrane irritation for swimmers. Make sure any cleaning hardware is not malfunctioning.

Community Q&A

Question

Is a clarifier also known as a shocker?

Community Answer

No. Shock kills bacteria, while clarifier binds small particles together to make them able be picked up better by the filter. You often need both to clear up a pool.
Question

What can cause my pool to get cloudy when I clean it?

Community Answer

Tree seeds, pollution in the air, pollen, fuzzies from trees, unclean filters etc. In 1980, three weeks after Mt. St. Helens volcano blew, many people experienced a black oil-type of ring around their pools; it was from the ash being carried by the wind. If you have neighbors who use burning barrels, this may cause film on a pool.
Question

Can I swim in cloudy pool?

Community Answer

This would not be a good idea, as you could get very sick from it. It would be best to wait until the water is clear.

Warnings

Do not attempt to swim in the pool until you have tested the water and have verified that the water is safe against any manufacturer instructions for clarifying or water treatment solutions. These solutions are concentrated and intended for use on thousands of gallons of water and can cause chemical burns if used improperly.

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Wear gloves and goggles when handling pool treatment chemicals.

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Make sure anyone who has access to the pool does not enter while it is being treated.

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